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Full text of "Handbook Of Chemical Engineering - I"

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Introduction.  This subdivision will fall into the following sub-heads: Separation of solids from solids; separation of solids from liquids; liquids from liquids; and the separation of solids from gases. The separation of liquids from liquids is also covered under "Distillation."
Separation of Solids from Solids.  Since the preceding section dealt with screening it is natural to begin this section with separating devices employing screens or apertures. With respect to separation by an aperture there are numerous devices employing a fixed aperture where the material to be separated has a hard and soft part as cotton bolls, raisins, cherries, etc. In the case of the separation of cotton from the boll the description of the earliest gin invented by Eli Whitney will show how an aperture or apertures is made use of to free the cotton from the seed. The fiber rests upon an inclined grid into the apertures of which project a series of saw-toothed discs mounted upon a revolving shaft. The saw-toothed discs catch the cotton and pull it away from the seed and since the grid apertures are smaller than the seed the latter cannot pass through them and when clean make their way out of the device by rolling down the inclined surface of the grid.
Raisin Seeder.  The elements for one device of this kind are a cylinder mounted with closely spaced pins placed radially. The spacing of the pins is smaller than any thickness of the seed. The other elements of the seeder are a hopper in contact with the pin mounted cylinder, means for squeezing the raisin into the pins of the cylinder as by a flexible or flexibly mounted roller or rollers. Since the pins are so closely mounted that the seed cannot be squeezed in between them only the meat of the raisin is pushed into the interstices and the seeds project above the pin cylinder. Means are provided for removing the seed as by a scraper or toothed roller and finally means for removing the meats by a saw-toothed scraper. The operation of the household cherry stoner is too familiar to need description.
Separation by Screening.  A description of the mode of handling wheat in a large flour mill for cleaning and separating will illustrate the possibilities of separation by screens. Since work of this kind is done on a type of screen known as a separator a description of this machine is necessary for understanding the the ensuing account of the separating operations. Figure 1 shows a common type of separator, the wheat entering the top and first passing under the winnowing influence of the fan shown at the top of the figure. From this point it proceeds downward on to the screens. In the separator of the figure there are two batteries of screens, three high, which oscillate in opposition to one another so as to produce balance and eliminate vibration. The pair of actuating eccentrics are shown at A and B. The two batteries of screens slope in opposite directions. To overcome
1 Consulting Engineer, 409 Boston Building, Denver, Colo.